Process for the production of aromatic nitriles



1969 0. TH. A. HUIBERS 3,479,385

PROCESS FOR THE PRODUCTION OF AROMATIC NITRILES Filed 001;. 29, 1965Flue Gas 7. he j W /5\ N? 'l J l H e 22 N Separator 20 23 Catalys? /6Regenerqio Reactor /3 24 26 5 H2 7 2 Seporofor m? 27 /7 Catalyst 28 Air,2 29

Hydrocarbon Ammonia Ammonia Recovery /30 Water INVENTOR Derk Th. A.Huibers BYflhfz f W ATTORNEY United States Patent US. Cl. 260-465 7Claims ABSTRACT OF THE DISCLOSURE A process for producing a polynitrilefrom an aromatic hydrocarbon containing at least two alkyl substituentgroups, the alkyl group having 1-3 carbon atoms, wherein the hydrocarbonis contacted in the gaseous phase with ammonia in the presence of anoxide catalyst at a temperature of 400-500 'C., a contact time of 0.0130seconds and a catalyst-on-stream time of less than 30 minutes. Theprocess is particularly applicable to producing terephthalonitrile fromp-xylene.

This invention has to do with a process for forming aromaticpolynitriles, particularly for forming terephthalonitrile from p-xylene.

Catalytic conversion of hydrocarbons and ammonia to nitriles hasreceived considerable attention in recent years. For example, toluenehas been converted to benzonitrile .in the presence of ammoniationcatalysts such as associations of molybdena and vanadia. However, whileconversion of xylenes to the corresponding tolunitriles has beenaccomplished with reasonable success, conversion of tolunitriles to thecorresponding dinitriles has been unsatisfactory.

In prior processes, temperatures as high as about 700 C. have beenrequired. At such temperatures, there has been a rapid loss in catalystactivity, decrease in conversion selectivity and substantial cokeformation on the catalyst, all cooperating to reduce the yield ofdesired product.

Another process has also been developed recently for producing nitriles.This is generally referred to as ammoxidation, wherein oxygen is used asa charge material with hydrocarbon and ammonia. Typical of ammoxidationcatalysts are associations of bismuth oxide and molybdena. With oxygen,as in the form of air, oxygenated products are formed, making necessarya purification system to effect separation of desired nitrile andoxygenated contaminants.

Since aromatic polynitriles such as phthalonitrile andterephthalonitrile are of value, for example, in the dyestuff and fiberindustries, respectively, it would be advantageous to have available anefficient and effective process for converting xylenes to aromaticpolynitriles. The present invention is directed to just such a process.

It is an object of the present invention, therefore, to provide aselective catalytic process for forming aromatic polynitriles. Anotherobject is to provide such a process substantially free from cokeformation. Still another object is to provide such a process in whichtemperatures lower than conventional ammoniation temperatures areemployed. A further object is to provide an effective processsubstantially free from formation of undesired oxygenated products.Another object is to provide a continuous process so characterized. Amore specific object is to provide a process for converting xylenes tothe corresponding dinitriles, and particularly to terephtholonitrile.Other objects will be apparent from the following description.

3,479,385 Patented Nov. 18, 1969 In accordance with the presentinvention, there is provided a process for preparing aromaticpolynitriles, comprising: contacting an aromatic hydrocarbon withammonia, in gaseous phase, at a temperature from about 400 C. to about500 C. in the presence of an oxide catalyst, with a contact time of fromabout 0.01 second to about 30 seconds and a catalyst-on-stream time ofless than about 30 minutes. The aromatic hydrocarbon is one which is:stable to thermal decomposition, in the vapor phase at said reactionconditions, and represent by the general formula L ArR wherein Ar is anarylene group, R is an alkyl group having from 1 to 3 carbon atoms, andn is a small whole number, at least 2.

Aromatic hydrocarbons useful herein include: xylenes; tri-, tetra-,pentaand hexa-rnethyl benzenes; diethyl and related polyethyl benzenes;polypropyl benzenes; diand further-methylated, -ethylated, and-propylated naphthalenes anthracenes, etc. Preferred herein are xylenesand, particularly, p-xylene. Thus, the arylene group can be a benzene,naphthalene, anthracene, etc. ring.

As indicated above, the catalysts used herein include those known asammoniation catalysts, that is, catalysts used in the conversion ofhydrocarbons and ammonia to nitriles without substantial addition ofoxygen to the reaction charge. Such catalysts include associations ormixed oxides of molybdenum and/ or tungsten, and of vanadium, ironand/or cobalt. Molybdena/vanadia catalysts are effective catalysts inthe process of this invention.

Ammoxidation catalysts can also be used in the present process althougha free oxygen-containing gas is not used as a charge material. Typicalof such catalysts are the bismuth oxide/molybdena catalysts referred toabove.

In addition to such catalysts, I have also found that the following canbe used:

associations of molybdena and ferric oxide, as

z s s m associations of stannic oxide and vanadia, H SiMo O Bi O(H4SiMOO40), and Bi O4 5(H PMO 2O40).

The catalyst can be used per se, or can be supported on or mixed with aninert support such as Carborundum, pumice, clay or the like, in whichcase texture, surface area and pore diameter can be suitably controlled.The inert support can serve to provide mechanical strength and abrasionresistance to the catalyst. The catalyst, with or without support, canbe in the form of fine particles such as suitable for use in a so-calledfluidized reactor bed, pellets, granules, etc.

Essential features in the formation of the aromatic polynitriles arecontact time and catalyst-on-stream time. Contact time is the period oftime during which a unit volume of the reactants is in contact with aunit volume of catalyst. Catalyst-on-stream time is the time duringwhich the catalyst is in use in converting an aromatic hydrocarbon andammonia to the desired polynitrile, before it is reactivated orregenerated. It has been found that the contact time should be fromabout 0.01 second to about 30 seconds, preferably 0.1-l0 seconds, with acatalyst-on-stream of less than about 30 minutes, preferably less than10 minutes.

In prior processes brief contact times of the order of those used hereinhave been employed; however, catalysts have been maintained on streamfor several hours before reactivation or regeneration. In suchprocesses, aromatic mononitriles have been formed, with little or noformation of polynitriles. Additionally, the much longer on-stream timesat elevated temperatures have resulted in substantial coke formation onthe catalyst. Removal of the coke by burning the same with oxygen hasinterfered with the heat balance of the process and, in some instances,has resulted in damage to the catalyst.

In the presence of ammonia and hydrocarbon, mixed oxide catalysts oftransition metals are reduced. The reduced form is considerably lessactive than a more oxidized form, which need not necessarily be thehighest oxidation level of the oxide catalyst.

In the present process, the relatively short catalyston-stream timesmake possible maintenance of a high catalytic level, also avoiding anysubstantial coke deposit on the catalyst. Reactivation of the catalystwith a free-oxygen containing gas such as air or oxygen can beaccomplished readily, therefore, in a briefer period of time than in theprior processes alluded to above. In reactivating a used catalyst, it isadvantageous to use a suflicient quantity of oxygen to convert the usedcatalyst to an oxidized. state.

In the present process, an excess of ammonia is generally used inrelation to the stoichiometrical quantity of aromatic hydrocarbon.However, from about 0.5 :1 to about 12:1 volumes of ammonia can be usedper volume of xylene, especially ratios of about 1:1 to 6:1. It will beunderstood that larger ratios of ammonia to hydrocarbon are used as anAr group is more substituted with R groups than is the benzene ringsubstituted with methyl groups to form xylenes. It is economical,however, not to use a large excess of ammonia or of an aromatichydrocarbon, particularly in a continuous operation such as describedbelow in order to simplify recycling of a reactant.

The aromatic hydrocarbon reactant can be used per se or can be presentin admixture with other hydrocarbons inert in the reaction, such asparafiin or benzene. Preferably, the reaction system is diluted with aninert gas such as nitrogen, steam or water vapor. Thus, it has beenfound that the use of steam or water vapor has the advantage ofretaining the catalyst oxygen for a longer period of time than when thearomatic hydrocarbon is converted in the substantial absence of addedsteam or water vapor. Preferably, from about 3 .to about 10, andespecially about 5 volumes of steam are used per volume of totalreactants, namely, aromatic hydrocarbon and ammonia.

The use of a diluent in the process of this invention is advantageous inseveral respects. With a diluent, the process is operated with a netproduction of hydrogen and no net heat generation. The diluent alsoserves to: carry off process heat thereby obviating the need forinternal heat transfer surface, and diminish the partial pressures ofthe reducing compounds charged and formed.

Reacting temperature for forming a polynitrile is an important feature.Temperatures below about 400 C. are to be avoided since yields areinsuflicient. Temperatures above about 500 C. are also to be avoided,since yields are reduced by virtue of decomposition of reactants andproducts. Preferably, temperatures of the order of 450- 460 C. areemployed.

Reaction pressures generally range from about 1 to about atmospheres,absolute. Pressures of 1.5-2 atmospheres, absolute, are preferred.

The process can 'be conducted intermittently or continuously, with thelatter preferred. The latter is particularly advantageous and isillustrated generally in the accompanying drawing which constitutes aschematic flow diagram. In the drawing, for example, p xy1ene in line 10and ammonia in line 11 are mixed in line 12 and are charged to reactor13, wherein they are in reaction in the presence of a catalystintroduced into 13 from line 14. Reactor 13 can comprise a lowerpreheating zone and an upper reaction zone. Catalyst and reactants flowconcurrently up through reactor 13, with catalyst being removed throughline 15 to an upper portion of reactivator or regenerator 16. Air orother suitable active oxygen-containing gas is introduced from line 17to a lower portion of regenerator 16 and is in countercurrent contactwith the catalyst for reactivation. Gases formed during reactivation,broadly termed flue gas, are removed through line 1-8. Reactivatedcatalyst is recycled from 16 through line 14 to reactor 13. As shown,make-up catalyst can be added to line 14 from line 19, and catalystfines or catalyst rejected for any reason can be removed through line20.

Reaction products comprising terephthalonitrile, tolunitrile, hydrogenand water, together with unreacted ammonia, are removed from reactor 13through line 21 to separator 22, from which the nitriles are dischargedthrough line 23. Terephthalonitrile and tolunitrile can be separatedfrom one another and tolunitrile can be recycled (not shown) with thehydrocarbon in line 10. Hydrogen, water and ammonia are removed from 22through line 24 to hydrogen separator 25. Hydrogen is removed from 25via line 26. Ammonia and water are taken from separator 25 through line27 and can be passed through line 28 to line 12 for use in reactor 13 orcan be passed through line 29 to ammonia recovery unit 30. Ammonia isremoved from unit 30 through line 31 and is combined with ammonia chargein line 11. Water is removed from unit 30 through line 32. Diluent canalso be charged through line 33.

During reactivation or regeneration of the catalyst, as in unit 16 ofthe drawing, the temperature should be controlled lest the catalyst bedamaged. The maximum temperature to be used will vary with catalystsemployed. Air is preferred as an oxidation medium; however, oxygen andother free oxygen-containing gas can be used satisfactorily.

The following typical, and non-limiting, examples illustrate theinvention.

EXAMPLE 1 A series of runs was conducted with p-xylene, ammonia and amolybdena/vanadia catalyst for-med by the following procedure.

To a slurry of 187 grams of vanadia in 700 ml. of distilled water,heated on a hot plate to C., was slowly added 379 g. of oxalic aciddihydrate. The solution turned blue and carbon dioxide escaped whilevanadia dissolved with formation of vanadyl oxalate:

After all the vanadia had gone into solution, 181 g. of ammoniamolybdate in 500 ml. of distilled water was added slowly with agitation.A black color developed but no precipitate formed. The pH of thecombined solutions was 1.6. It was raised to 6.3 by the gradual additionof concentrated aqueous ammonia (190 ml.). After addition of about ml.of ammonia, the pH had increased to about 4.4, and a black precipitatewas formed. When at this value agitation was stopped, the entire mass inthe reaction vessel used solidified due to the formation of a metastablemicel structure. The mass could be liquified again upon continuing theagitation. The slurry was poured into baking dishes and left overnight.Evaporation of the aqueous phase was done very slowly; during 5 days,the temperature was brought up gradually to 100 C., and so maintainedfor 24 hours. Finally, the catalyst was calcined in a mufile furnace.The temperature of the muflle furnace was brought in 3 /2 hours from 40C. to 400 C., and kept at 400 C. for one hour. The catalyst mass wasthen cooled and broken in pieces. The fraction of 6-9 mesh was used forthe series of runs.

All runs were carried out with the same catalyst charge comprising 123.2grams (200 ml.) of the molybdena/ vanadia catalyst in a process schemesuch as shown in the drawing. Product was accumulated during 30 minuteperiods and was designated Sample A; then, for one or two subsequent 30minute periods, product was also accumulated and designated Samples Band C, respectively. The

catalyst was reactivated with air after each B run of a series of A andB runs, or after a C run in a series of ABC runs.

The reaction efiluent was trapped in two cooled flasks.Terephthalonitrile (TPN), formed as a product, is wholly insoluble inxylene; the product crystals were filtered, washed with hexane, driedand weighed. The mother liquor and hexane washings were combined andanalyzed for tolunitrile (TN) by gas chromatography. The results areshown in Table 1 following.

In Table 1, x/a represents the mole fraction of pxylene converted top-tolunitrile and y/a represents the mole fraction of p-xylene convertedto terephthalonitrile.

approximately parts of terephthalonitrile are produced per 1000 parts byweight of catalyst.

EXAMPLE 3 TABLE 1.AMMONIATION OF p-XYLEN E [30 min. runs] Feed (1gas/min. at temp.) Reactor Product (g.) Conv. (mole percent) Contact TN'IPN Temp, C. p-Xylene NHs N2 H2O Total Temp., 0. time, sec. TN TPN 100x/a 100 y/a.

0. 0421 1. 54 460 3. 18 1. 00 2. 6 16 39 23 0. 0 496 l. 55 460 3. l3 1.71 0. 55 24 7 25 0. 0453 1. 55 460 3. 15 1. 54 0. 4 24 6 25 0.0421 4.04460 1. 21 0. 70 2. 0 12 25 0. 0438 4. 04 460 1. 21 l. 14 1. 1 18 16 260. 0386 5. 29 460 0. 93 0. 69 2. 5 13 42 26 0. 0455 5. 30 460 0.93 1.13 1. 1 17 15 26 0. 0386 7. 79 460 0. 63 0. 79 1. 6 15 27 26 0. 0462 7.80 460 0. 63 0. 52 0. 55 8 8 25 0. 0368 7. 79 460 0. 63 0. 51 1. 10 2325 0. 0438 7. 79 460 0. 63 0. 59 0. 9 9 13 25 0. 0398 7. 79 490 0. 600.46 2. 5 8 25 0. 0461 7. 80 490 0. 60 0. 56 0. 3 8 4 25 0. 0421 2. 06460 2. 38 0. 70 3. 35 12 25 0. 0438 3. 76 460 1. 30 0. 54 0. 65 9 10 230. 0776 5. 38 460 0. 91 1. 45 3. 7 13 30 21 0. 0743 5. 69 460 0. 84 1.07 0. 2 10 2 (A=1irst half hour, B=second half hour, 0 =third half hour)The results shown in Table 1 reveal that conversion of p-xylene toterephthalonitrile is substantially greater during an initial 30 minuterun, than during a subsequent 30 minute run. For example, in Run 76A,the mole conversion is 39 percent; whereas, in Run 76B, it is only 7percent. The same pattern is revealed for A and B of Runs 77 through 83,inclusive. The data indicate that the catalyst is reduced in activitywith respect to formation of terephthalonitrile, but has greateractivity for the production of tolunitrile. This is due to oxygen lossof the catalyst.

With very short contact times, the catalyst activity can be maintainedfor relatively longer on-stream times but conversion is meager anduneconomical. If contact time is very short, catalyst-on-stream time canbe extended even beyond about 30 minutes, but the results are similarlyuneconomical. With longer contact times, as 5-30 seconds,catalyst-on-stream time is of shorter duration but conversion ofaromatic hydrocarbon to desired polynitrile is higher. For example, itis to be understood that catalysts employed herein differ in activity.Thus, contact times of 5-30 seconds are preferred when using Fe O Mo Orather than briefer contact times.

EXAMPLE 2 A mixture of p-xylene and ammonia was passed downwardlythrough a static bed of the molybdena/vanadia catalyst described inExample 1, at 460 C. at a contact time of about 3 seconds. During thefirst 10 minute period, the product was predominantlyterephthalonitrile. Then, a mixture of terephthalonitrile andtolunitrile was formed. Finally, after about one hour, substantiallyonly tolunitrile was formed. When about 30 moles of ammonia are chargedper mole of p-xylene, about 8 parts by weight of terephthalonitrile areproduced per 1000 parts by weight of catalyst. When, however, part ofthe ammonia is replaced by nitrogen diluent such that the mole ratiop-xylene/ammonia/N is 1/ 3/ 30 and the same contact time and the sameon-stream time are employed,

It will be evident from the foregoing that an elfective process has beenfound for the production of aromatic polynitriles. Terephthalonitrile,for example, is formed from p-xylene and can be used for the formationof terephthalic acid, which is of importance in the manufacture ofsynthetic fibers. Phthalonitrile can be formed from o-Xylene, and can beused in the formation of phthalocyanine dyes. Other uses will be evidentto those familar with the art.

Many modifications and variations of the invention as set forth abovemay be made without departing from the spirit and scope thereof.Consequently, the appended claims are intended to include suchmodifications and variations.

I claim:

1. In the production of an aromatic nitrile by contacting ammonia withan aromatic hydrocarbon in the gaseous phase, in the presence of anoxidized form of an oxide catalyst selected from the group consisting ofammoniation catalysts and ammoxidation catalysts, the aromatichydrocarbon being selected from the group consisting of alkylsubstituted benzene, alkyl substituted naphthalene and alkyl substitutedanthracene wherein the alkyl group has 1-3 carbon atoms and there are atleast two alkyl substituent groups, the improvement for producingaromatic polynitriles comprising: effecting said contacting of ammonia,aromatic hydrocarbon and catalyst in the absence of molecular oxygen ata temperature from about 400 C. to about 500 C., a contact time of fromabout 0.01 second to about 30 seconds and a catalyst on-stream time ofno longer than about 30 minutes, followed by removal of said catalystfrom on-stream, contact of the said removed catalyst with a molecularoxygencontaining gas to regenerate the same and recycling saidregenerated catalyst to the on-stream.

2. The process defined by claim 1 wherein the aromatic hydrocarbon is axylene.

3. The process as defined in claim 1 wherein the arcmatic hydrocarbon isp-xylene.

4. The process defined by claim 1 wherein the catalystone-stream time isfrom about 0.01 second to about 10 minutes.

- 5. The process defined by claim 1 wherein the contact time is fromabout 0.1 second to about 10 seconds.

6. The process defined by claim 1 wherein the contact time is from about0.1 second to about 10 seconds and the catalyst-on-stream time is fromabout 0.1 second to about 10 minutes. 1

7. The process defined by claim 1 wherein the temperature is from about450 C. to about 460 C.

8 References Cited UNITED STATES PATENTS OTHER REFERENCES 10 Denton eta1, Industrial and Engineering Chemistry, vol.

42, No. 5, May 1950, pp. 796-80 0.

JOSEPH P BRUSTQPrimary Examiner

